This is the first of two papers in which we propose an evolutionary route for the transition from sensory processing to unlimited experiencing, or basic consciousness. We argue that although an evolutionary analysis does not provide a formal definition and set of sufficient conditions for consciousness, it can identify crucial factors and suggest what evolutionary changes enabled the transition. We believe that the raw material from which feelings were molded by natural selection was a global sensory state that we call overall sensation, which is a by-product of the incessant activity of the highly interconnected nervous systems that characterize all neural animals. We argue that global sensory states generated limited experiencing once they became coupled to the simplest kinds of nervous-system-mediated learning, a coupling that occurred in the most ancient taxa of neural animals, which were similar to present-day cnidarians and ctenophores. In such animals, limited experiencing involves a small number of persistent global sensory states. These sensory states, however, do not have a function and do not act as motivational states. As we argue in the next paper, with the evolution of associative learning they evolved into systems that gave animals basic consciousness